Electrical cable

ABSTRACT

An electrical conducting cable for submersible motors adapted for use in high temperature, high pressure oil wells. The cable includes separately insulated conductors disposed within an epichlorohydrin rubber jacket. The conductors are insulated with a layer of high temperature, high molecular weight, heat stabilized polypropylene as the primary insulation. The jacketed cable unit is protected by an outer armor formed of a high temperature, high molecular weight, heat stabilized, polypropylene. The cable thus formed is flexible, abrasion resistant, solvent resistant, liquid impervious, heat in sensitive and unaffected by well environment.

United States Patent 1191 11 3,710,007 Hoeg et al. 1451 Jan. 9, 1973154] ELECTRICAL CABLE 3,614,300 10 1971 Wilson ..l74/ll0R [75]Inventors: Donald F. Hoeg, Mount Prospect,

111.; Leo V. Legg, Tulsa, Okla; Donatas Tijunelis, Buffalo Grove,

Ill

Assignee: I Borg-Warner Corporation, Chicago, 7

Filed: Dec. 16, 1971 Appl. No.: 208,624

116,174/120 R, 120 SR, 120 AR References Cited UNITED STATES PATENTS1/1967 Brown ..l74/ll0R Primary Examiner--E. A. Goldberg AttorneyWilliamS. McCurry et al.

[57] ABSTRACT An electrical conducting cable for submersible motorsadapted for use in high temperature, high pressure oil wells. The cableincludes separately insulated conductors disposed within anepichlorohydrin rubber jacket. The conductors are insulated with a layerof high temperature, high molecular weight, heat stabilizedpolypropylene as the primary insulation. The jacketed cable unit isprotected by an outer armor formed of a high temperature, high molecularweight, heat stabilized, polypropylene. The cable thus formed isflexible, abrasion resistant, solvent resistant, liquid impervious, heatin sensitive and unaffected by well environment.

4 Claims, 2-Drawing Figures 15(POLY PROPYLENE) 19(POLY PROPYLENE)PATENTEDJAN 9 I975 15 (EPICHLOROHYDRIN RUBBER) CONDUCTOR 15 (POLYPROPYLENE) 19 (POLY PROPYLENE) INVENTOQS DOA/4L0 l-THOEG 00/ 4745T/Jl/A/EZ/S LEO l4 L566 ATTORNEY ELECTRICAL CABLE BACKGROUND OF THEINVENTION This invention relates to electrical cable. More particularly,it relates to electrical cable utilized to deliver electrical energy tosubmersible motors adapted for use in high temperature, high pressureoil wells.

Submersible pumps used in oil, mineral and water wells normally includea prime mover in the form of an electric motor directly coupled to thepump and disposed deep within the well. It is, therefore, necessary toprovide an electrical connection between the motor and a source ofelectrical energy at the surface. This is normally accomplished by theuse of an electrical conducting cable which extends between the sourceof electrical energy and the motor.

In many instances, the motors operate at relatively high power levels,in some cases exceeding 200 horsepower. Normally, the motors used are ofthe threephase type and the associated cable includes three separateelectrical conductors.

The electrical cable must have adequate current carrying capability andmust be of sufficient dielectric strength to prevent electrical losseseven under the adverse environmental conditions usually found within thewell. The environmental conditions of the well vary generally dependingupon geographical location. In some cases the well fluid is highlycorrosive and in many instances well temperatures exceed 250F. Most oilwells contain dissolved H 8 gas, carbonates, salts and large volumes ofoil. Additionally, the wells are quite deep, averaging 8,000 to 10,000feet. The electrical cable must possess enough physical strength toallow insertion of the motor and cable to these depths and the outersurface of the cable must resist the abrasion associated with insertion.Since the cable is normally wound upon storage or transportation reels,it must possess the additional property of flexibility so that it willresist physical damage caused by reeling.

Typical cable construction presently being utilized includes threeconductors of stranded copper separately insulated and helically woundto form a single unit. The stranded conductors are insulated with amaterial of high dielectric strength such as polyethylene orpolypropylene. The helically wound and insulated conductors are sheathedin an extruded jacket of nitrile rubber surrounding the insulatedconductors.

One common form of jacketed cable is covered with an outer armor in theform of a continuous wrapped band of metallic material. This band islapped as it is wound. The armor provides abrasion resistance. Usually,the armor is formed of steel or bronze; however, in many specialapplications, such as wells which are excessively corrosive, stainlesssteel or exotic metals such as monel metal must be used.

The equipment required to wind the metallic band to form the armor isexpensive, complex and slow. Further, splicing of the armor cable in thefield is complicated because of the presence of the metallic outerlayer.

Polyethylene has also been employed to a limited extent as the outerarmor, but it has been found that the same does not stand up underseverely high temperatures.

Proper material selection for the cable armor has always presenteddifficulties. Many different armor materials must be utilized dependingupon the well conditions and no single cable construction has been foundsuitable for universal application. This is especially true for thedeep, high pressure and high temperature wells.

Electrical power cables constructed as previously described which havebeen used in high temperature, high pressure oil wells, fail because oftemperature distortion of the thermoplastic cable components, corrosionof the armor, or chemical and solvent attack of the elastomer jacket.Since most oil wells contain dissolved l-I S gas, carbonates, water,salts and large volumes of oil, no single material has the resistance tosolvents, heat and pressure to operate for prolonged periods in such anenvironment.

An additional problem encountered by cables in such an environment isdeformation under load. The cables are subject to both compressive andtensile forces and, under high temperatures, there is a marked tendencyfor the jacketing to deform resulting in dislocation of the conductorsand phase to phase or phase to ground short circuitry.

Rupture of the armor due to swell of the jacket is another example ofdeformation which occurs in such an environment. Rupture of the totalconstruction also occurs during retraction of thecable from the well asa result of the depressurization of fluids which have permeated thecable.

These and other associated difficulties have clearly dictated the needfor an improved impermeable, environment insensitive cable construction.

Accordingly, it is the principal object of the present SUMMARY OF THEINVENTION The present invention relates to an improved multicomponentelectrical cable for submersible motors adapted for use in hightemperature, high pressure oil wells. More particularly, it relates to acable construction which includes an outer armor of high temperature,high molecular weight, heat stabilized polypropylene, an inner jacket ofepichlorohydrin rubber and a high temperature, synthetic, organicinsulator surrounding the electrical conductors.

The polypropylene used for the outer armor is of a type not normallyused for wire insulation because of its processing difficulties butpossesses a maximum of heat resistance especially with respect to hightemperature creep characteristics. An example of a suitable armormaterial is a high molecular weight polypropylene homopolymer of highisotactic level.

The epichlorohydrin rubber used for the jacket is compounded for theminimum of oil and water permeability and swell.

The type of insulator disclosed for use in high temperature, highpressure oil wells is a high temperature, high molecular weight, heatstabilized, polypropylene which is an excellent electrical insulator atelevated temperatures when unaffected by oil. A polypropylenehomopolymer of predominantly isotactic structure has been found to be agood choice.

The outer armor of polypropylene is water insensitive and waterimpermeable so that it protects the epichlorohydrin rubber jacket. Theepichlorohydrin rubber jacket is insensitive to any oil which may havepermeatedthe polypropylene armor and in addition is highly oilimpermeable providing a barrier which protects the polypropyleneinsulation. The result is a minimum of water or oil permeation, or anyeffect therefrom.

These and other objects and advantages of the present invention willbecome apparent with reference to the following description andaccompanying drawings.

DESCRIPTION OF DRAWINGS FIG. 1 is a fragmentary perspective view of asection of electrical conducting cable for submersible motorsillustrating various features of the invention.

FIG. 2 is a cross-sectional view of the cable of FIG. 1 taken generallyalong the lines 22 of FIG. 1.

DESCRIPTION OF ILLUSTRATED EMBODIMENTS Referring now to the drawing,there is shown a multicomponent electrical conducting cable for asubmersible motor designed for use in high temperature, high pressureoil wells which is illustrative of the principles of the presentinvention.

FIG. 1 shows a cable section which includes conductors 11, a resilientjacket 13 and an outer armor 15.

Each conductor 11 is formed of stranded wire 17 helically wound toprevent separation of strands. These separate strands may be tinned tominimize chemical interaction between the conductor and the insulatingmaterial.

In the illustrated embodiment each conductor includes seven strands. Thenumber of conductors, the diameter of the conductor and number of wiresis, of course, dependent upon the load carrying capabilities requiredfor a particular cable application. It should additionally be noted thatany suitable conducting material may be used, such as for example,copper, aluminum, etc.

Each wound set of wire strands forms a single conductor and isseparately insulated by an insulation layer 19. The conductor insulation19 is formed of a high temperature, organic, synthetic material of highdielectric strength. One example found to be satisfactory for thispurpose is a high temperature, high molecular weight, heat stabilizedpolypropylene.

If the conducting material is copper the polypropylene conductor willhave to be copper stabilized in addition to being heat stabilized.Copper stabilization of olefin rubbers and polymers is well-known in theart and can be accomplished in a manner such as disclosed in U. S. Pat.Nos. 3,535,257 or 3,549,572 or any other acceptable method of copperstabilization. If the conducting material is other than copper otherstabilization may be required. An extruded covering of such an insulatormay be used to form the conductor insulation.

A preferred embodiment of a high temperature, high molecular weight,heat stabilized polypropylene homopolymer insulating material iscommercially available under the trade name Avisun I046 from AmocoCorporation. This material has been found to possess the followingphysical properties:

Molecular Weight High as evidenced by reduced viscosity of 11 3.5 dl/gtested in Decalin at 135C.

Specific gravity 0.90 0.91 at 23C (ASTM-D-7 Flow Rate at 230C, 2,160gram load, 5.0 grams per 10 minutes (ASTM-D-1238-65T) Deflectiontemperature 230F (ASTM-D-64 8-6 I Deformation under load 3.5% at 2000PSI (24 hrs.

at 50C) (ASTM-D62 l-64) Water Absorption 0.01% (ASTM-D-S -63) FlexuralModulus 180,000 PSI (0.05 in/min CHS) (ASTM-D-790-66) As previouslymentioned this polypropylene may have to be modified for copper or othermetal stabilization depending upon the conductive material which maysomewhat alter its physical properties.

The wound conductor unit is disposed within the jacket 13 which iscomprised of a high molecular weight epichlorohydrin rubber compoundedfor the minimum of oil and water permeability and swell. This jacket maybe extruded about the wound conductors and preferably is formed to fillinterstices 23 between adjacent conductors.

One preferred embodiment is a formulation of epichlorohydrin compoundedof the materials and in approximately the ratios as follows:

at 66PSI Parts/ I00 parts Trade Name Material of rubber Available fromHerclor High Molecular Weight 100.0 Hercules, lnc. epichlorohydrinrubber Span 60 Surface active agent I.5 Atlas Chemical comprised ofpartial Industries esters of hexitol anhydrides Dyphos XL Di-Basic LeadPhosphite l0.0 National Lead (heat stabilizer) Company N B C Nickeldibutyl dithio- 1.0 Du Pont carbamate (anti-oxidant) Cumate Copper,dimethyl dithio- 0.l25 R.T. Vanderbilt carbamate (accelerator) CompanyPheno- Phenothiazine 1.0 Fisher Scientific thiazine Company VulcanCarbon Black (filler) 30.0 Cabot Corporation Hi Sil Silica (filler) 10.0P.P.G. 233 Industries TIE-70 Plasticizers 0.5 Technical Processing, Inc.TP- Plasticizers l.0 Thiokol Chemical Corp. Azelaic Dispersant 4.0Eastman Organic Acid Chemicals NA-22 2 mercaptothiazoline l.0 Du Pont(accelerator) The extruded epichlorohydrin jacket completely fills thevoids formed about the separately insulated conductors. This precludesexposure of the insulation to well fluid and further prevents flow ofwell fluid along the cable length in the event that a rupture occurs atsome point along the outer armor l5 and the outer periphery of jacket13.

The jacket 13 of the cable is surrounded by the extruded outer armor 15formed of a high temperature, high molecular weight, heat stabilizedpolypropylene.

The polypropylene previously described for the insulating material is apreferred embodiment for the outer armor and has exhibited excellentheat resistance especially with respect to high temperature creepcharacteristics. When used for the outer armor it would not be necessaryto modify this polypropylene for copper or other metal stabilization.

The polypropylene used for the outer armor must have a very low watersensitivity to protect the epichlorohydrin jacket from any swellingwhich, in turn, would keep any traces of oil from attacking thepolypropylene primary insulation. This is necessary because whenunaffected by oil this particular polypropylene is an excellentelectrical insulator at the elevated temperatures at which it mustoperate in a high temperature, high pressure oil well.

The outer armor is preferably formed by extruding. The extruded armor isformed in surrounding relation to the jacketed cable unit as the cableunit progresses through an appropriate extrusion die. Thus, a completelysealed, fluid impervious armor is efficiently formed about the jacket 13which separates the jacket and the well fluid and protects the internalcomponents of the cable from physical and chemical damage.

The particular polypropylene described has a dielectric strength ofabout 650 to 750 volts per mil. It has excellent abrasion resistance andforms a smooth outer cable surface. It is resistant to the attack ofchemical agents such as H S gas, carbonates, salts and oil found withinthe well and provides a barrier against moisture, oils and greases. Ithas a water absorption of about 0.03 percent. Additionally, thispolypropylene retains its abrasion resistanceat both high and lowtemperatures and it has little, if any, environmental stress cracking.The polypropylene described is sufficiently resilient to allow reelingand unreeling of the motor cable without cracking the protective armor.

While polypropylene generally is somewhat sensitive to light and, undercertain conditions, suffers loss of dielectric strength, it has beenfound that the addition of darkening pigments as well as ultra-violetlight stabilizers to the polypropylene armor adequately protects thearmor from deterioration caused by exposure to light.

Use of a multicomponent cable such as that described provides a cableconstruction which is abrasion resistant, impervious to well fluids,flexible and unaffected by corrosive well environments and hightemperatures. Further, construction of the cable is simplified byextruding the armor onto the jacketed cable unit.

An example ofa well cable illustrating features of the present inventionhas been constructed. It includes three seven-wire stranded copperconductors, each of which is surrounded by a high temperature, highmolecular weight, heat and copper stabilized polypropylene insulationhaving an average thickness of 0.072 inch. The separate conductors arehelically wound to form a single unit. The conductors are jacketed withan epichlorohydrin rubber. The jacket thickness is 0.040 inch minimumaverage. The jacket is provided with a surrounding high temperature,high molecular weight, heat stabilized polypropylene armor having anaverage thickness of 0.085 inch.

As can be appreciated, the cable construction of the present inventionprovides an efficient and durable conducting unit for use in the adverseenvironment associated with high temperature, high pressure oil wells.The outer armor is easily formed and possesses the desirable physicalproperties making it suitable for application as a cable for submersiblewell motors.

While the epichlorohydrin rubber utilized for the jacket 13 was HerclorH (Hercules, Inc.), an epichlorohydrin homopolymer (poly (alphachloropropylene oxide)), other homopolymers of epichlorohydrin such asHydrin (B.F. Goodrich) are suitable for this application. Alsoepichlorohydrin rubbers prepared from epichlorohydrin and ethylene oxideare suitable for the jacket 13. These copolymers are sold under thetrade name Herclor C (Hercules, Inc.) and Hydrin 200 (B.F. Goodrich).

Various features of the invention have been particularly shown anddescribed in connection with the illustrated embodiments of theinvention. However, it must be understood that these particulararrangements are for illustrative purposes and that the invention is tobe given its fullest interpretation within the scope of the appendedclaims.

What is claimed is:

1. A multicomponent electrical cable adapted for use with a submersiblemotor, comprising at least one electrical conductor; a layer ofinsulating material surrounding said conductor formed of a hightemperature, synthetic, organic insulator; a resilient jacketsurrounding said insulation comprising an epichlorohydrin rubber of highmolecular weight and an outer armor surrounding said resilient jacketformed of a high temperature, high molecular weight, heat stabilizedpolypropylene.

2. A multicomponent cable as in claim 1 wherein said high temperature,synthetic, organic insulator is a high temperature, high molecularweight, heat stabilized polypropylene.

3. A multicomponent cable as in claim 2 wherein said high temperature,high molecular weight, heat stabilized polypropylene is also copperstabilized.

4. A multicomponent cable as in claim 1 wherein said conductor is copperand said high temperature, synthetic, organic insulator is copperstabilized.

2. A multicomponent cable as in claim 1 wherein said high temperature, synthetic, organic insulator is a high temperature, high molecular weight, heat stabilized polypropylene.
 3. A multicomponent cable as in claim 2 wherein said high temperature, high molecular weight, heat stabilized polypropylene is also copper stabilized.
 4. A multicomponent cable as in claim 1 wherein said conductor is copper and said high temperature, synthetic, organic insulator is copper stabilized. 